In the log processing industry it is becoming more common to automate the processing of raw logs into end products as automation offers significant advantages in terms of processing speed, reliability and cost.
In any processing operation handling raw logs, the logs are generally carried on conveyor belts between processing equipment that performs specific tasks on the logs. For example, in the processing of logs into sawed lumber, there are a number of steps involved. First, a group of raw logs are processed by singulating equipment that separates the group into individual logs. Each individual log is then processed by de-barking equipment. The logs are then fed on a conveyor past scanning equipment that analyses the cross-sectional area of each log and determines the orientation of the log for maximum recovery or conversion into saleable product. The log is then passed by orienting equipment that rotates the log to the desired orientation and onto the sawing equipment that cuts the log into raw lumber. An additional step may also involve cutting the logs into set lengths at some stage in the process.
An important part of the automatic processing of logs as outlined above is the orientation of the log to ensure maximum recovery. Equipment known as "flying vertical rolls" have been developed to adjust the orientation of logs in response to control signals generated by computer scanning equipment. The scanning equipment determines the angle to which a log should be rotated and the "flying vertical rolls" carry out the rotation of the log about its longitudinal axis. Conventional equipment comprises one or more pairs of spaced, upstanding spike rolls positioned on either side of a conveyor belt that define a passage through which a log to be rotated passes. The spike rolls are cylindrical members with radially extending spikes to grip and engage the log. The upstanding spike rolls are driven to rotate about their vertical axis thereby causing a log in the passage between the rolls to be advanced forward. The term "flying" in the name of the equipment refers to the fact that the log moves continuously through the passage even as it is being oriented. The spike rolls are also adapted for movement along the vertical axis about which they rotate. Moving a spike roll on one side of a log along the vertical axis while maintaining the position of the spike roll on the other side of the log causes the log to rotate to a new angle.
The "flying vertical roll" equipment does perform its job of rotating logs, however, it suffers from the significant drawback that accurate angular rotation of a log is difficult to achieve. The math needed to calculate the vertical movements of one or more spike rolls to rotate a log through a selected angle is quite complex. Because a log is essentially a tapered cylinder, rotating the log axis through a given angle by a tangential vertical movement at the perimeter of the log will depend on the circumference of the log at the point of engagement of the spike rolls. Therefore, it is necessary to take into account the feed speed of the log through the equipment and the time of engagement with the spike rolls so that the equipment will be able to calculate the circumference of the portion of the log that is engaged by the spike rolls when the log is to be rotated. Logs tend to have a curvature or "sweep" and this must also be taken into account when determining the vertical movement of a spike roll. It is easy to see that the accuracy of operation of the flying vertical roll is compromised when one considers that logs are asymmetrical and knots or other defects in the log will result in slippage of the log through the spike roll. The bottom line is that it is difficult to achieve optimum angular positioning of a log using the flying vertical roll.